The formation of adducts of 2,2-dimethylolalkanoic acid with anhydrides provides the intermediates for the production of the glycidyl esters of the present invention. For example, one mole of 2,2-dimethylolpropionic acid (DMPA) with phthalic anhydride yields a tricarboxylic acid adduct as follows: ##STR3##
U.S. Pat. No. 3,404,018 describes reaction products of hydroxy-carboxylic acids with liquid epoxy resins (commercial diglycidyl ethers of bisphenol-A). The hydroxy-carboxylic acids used include 2,2-dimethylolpropionic acid as well as adducts formed by reaction of polyols and dicarboxylic anhydrides.
Polyols included in the aforementioned patent are ethylene glycol, propylene glycol, butanediol, polyethylene glycols and glycerine.
Anhydrides included are maleic anhydride, succinic anhydride, dodecenyl succinic anhydride, phthalic anhydride, tetrahydrophthalic anhydride, hexahydrophthalic anhydride, dichloromaleic anhydride, and hexachloro-endomethylene tetrahydrophthalic anhydride.
The polyols are reacted with the anhydrides in a molar ratio of 1:1 under conditions whereby the anhydride ring is opened forming an ester group between one carboxylic acid group of the anhydride and one hydroxy group of the polyol but leaving the remaining carboxylic acid group and the remaining hydroxy groups unesterified.
The reaction of hydroxy mono-acids occurs with the epoxy group of the commercial liquid resin to form a hydroxy-ester with little or no esterification of the carboxyl group with the hydroxyls present in the molecule: ##STR4## where R.sup.1 is an aliphatic, cycloaliphatic or aromatic moiety derived from the monohydroxycarboxylic acid or polyol-anhydride adduct formed by reaction of a polyol and an anhydride.
A primary object of the present invention is to provide novel crosslinking agents for a variety of systems.
A further object of the present invention is to provide compositions useful in coatings and castings that resist the effects of weathering. SUMMARY OF THE INVENTION
The present invention provides polyglycidyl esters of the general formula (I) ##STR5## and compositions comprising said polyglycidyl esters.